1. Field of the Invention
The invention relates generally to a method and system for the computerized automatic segmentation of medical images. Specific applications are given for breast mammograms including the extraction of the skin line as well as correction for non-uniform exposure conditions, for hand radiographs, and for chest radiographs. Techniques include novel developments and implementations including noise filtering, local gray value range determination, modified global histogram analysis, region growing and determination of object contour.
2. Discussion of the Background
Although mammography is currently the best method for the detection of breast cancer, between 10-30% of women who have breast cancer and undergo mammography have negative mammograms. In approximately two-thirds of these false-negative mammograms, the radiologist failed to detect the cancer that was evident respectively. The missed detections may be due to the subtle nature of the radiographic findings (i.e., low conspicuity of the lesion), poor image quality, eye fatigue or oversight by the radiologists. In addition, it has been suggested that double reading (by two radiologists) may increase sensitivity. It is apparent that the efficiency and effectiveness of screening procedures could be increased by using a computer system, as a "second opinion or second reading" to aid the radiologist by indicating locations of suspicious abnormalities in mammograms. In addition, mammography is becoming a high volume x-ray procedure routinely interpreted by radiologists.
If a suspicious region is detected by a radiologist, he or she must then visually extract various radiographic characteristics. Using these features, the radiologist then decides if the abnormality is likely to be malignant or benign, and what course of action should be recommended (i.e., return to screening, return for follow-up or return for biopsy). Many patients are referred for surgical biopsy on the basis of a radiographically detected mass lesion or cluster of microcalcifications. Although general rules for the differentiation between benign and malignant breast lesions exist, considerable misclassification of lesions occurs with current radiographic techniques. On average, only 10-20% of masses referred for surgical breast biopsy are actually malignant.
It is apparent that the efficiency and effectiveness of screening procedures could be increased by using a computer system, which is capable of segmenting the mammogram into breast and non breast regions, detecting the skin line and perform enhancement that allows viewing of the complete dynamic range without loss in contrast. The enhancement techniques could improve detection of various lesions by increasing their conspicuity. Also, accurate segmentation allows for determination of the skin line. Although breast skin thickening may occur in a variety of benign disorders like edema, inflammation or scarring, it can also indicate underlying malignant disease and may be the only mammographic sign of an inflammatory carcinoma. .Also, such capabilities would be useful in other regions of the body, such as those examined by bone radiography and chest radiography.